Chemical vapor deposition methods are employed to form films of material on substrates such as wafers or other surfaces during the manufacture or processing of semiconductors. In chemical vapor deposition, a chemical vapor deposition precursor, also known as a chemical vapor deposition chemical compound, is decomposed thermally, chemically, photochemically or by plasma activation, to form a thin film having a desired composition. For instance, a vapor phase chemical vapor deposition precursor can be contacted with a substrate that is heated to a temperature higher than the decomposition temperature of the precursor, to form a metal or metal oxide film on the substrate.
Preferably, chemical vapor deposition precursors are volatile, heat decomposable and capable of producing uniform films under chemical vapor deposition conditions. In producing thin films by chemical vapor deposition processes, precursors that are liquid at room temperature, rather than solids, often are preferred.
The semiconductor industry is currently considering the use of thin films of ruthenium metal for a variety of applications. Many organometallic complexes have been evaluated as potential precursors for the formation of these thin films. These include, for example, carbonyl complexes such as Ru3(CO)12, diene complexes such as Ru(η3-C6H8)(CO)3, Ru(η3-C6H8)(η6-C6H6), beta-diketonates such as Ru(DPM)3, Ru(OD)3 and ruthenocenes such as RuCp2, Ru(EtCp)2.
Both the carbonyl and diene complexes tend to exhibit low thermal stabilities which complicates their processing. While the beta-diketonates are thermally stable at moderate temperatures, their low vapor pressures married with their solid state at room temperature make it difficult to achieve high growth rates during film deposition.
Ruthenocenes have received considerable attention as precursors for Ru thin film deposition. While ruthenocene is a solid, the functionalization of the two cyclopentadienyl ligands with ethyl substituents yields a liquid precursor that shares the chemical characteristics of the parent ruthenocene. Unfortunately, depositions with this precursor have generally exhibited long incubation times and poor nucleation densities.
U.S. Pat. No. 6,605,735 B2 discloses half-sandwich organometallic ruthenium compounds that have a cyclopentadienyl and pentadienyl group bonded to ruthenium. The cyclopentadienyl group can be mono-substituted or unsubstituted. The pentadienyl group can be mono-, di- or tri-substituted or unsubstituted. Certain substitution patterns are specifically excluded. It is stated in the patent that the inventors conducted extensive studies and found that the decomposition temperature of a ruthenocene can be lowered by substituting one of the cyclopentadienyl rings by linear pentadienyl. By introducing a single lower alkyl group into the cyclopentadienyl ring, it is stated in the patent that the half-sandwich organometallic ruthenium compounds have been found to be liquid at room temperature and exhibit favorable vaporization and decomposition properties. These compounds are used for producing a ruthenium-containing thin film by chemical vapor deposition.
In developing methods for forming thin films by chemical vapor deposition methods, a need continues to exist for chemical vapor deposition precursors that preferably are liquid at room temperature, have relatively high vapor pressure and can form uniform films. Therefore, a need continues to exist for developing new compounds and for exploring their potential as chemical vapor deposition precursors for film depositions. It would therefore be desirable in the art to provide a chemical vapor deposition precursor having a high nucleation density and producable with high yields.